In the conventional heap leaching of copper sulfide containing minerals (including chalcopyrite ores), mined ore is stacked into heaps, aerated through direct injection of air via aeration pipes extending into the heap and/or by natural convection through exposed areas of the heap, and irrigated with an acid solution for extraction of copper into solution. The copper is subsequently recovered from the acid solution by a range of recovery options including solvent extraction and electrowinning (SX/EW), cementation onto more active metals such as iron, hydrogen reduction, and direct electrowinning. The acid solution is regenerated and recycled through the heap to leach more copper from the ore in the heap. The ore in the heap may comprise agglomerates of fragments of ore. Leaching may be assisted by the addition of ferrous and sulfur oxidizing microorganisms.
Generally, heap and dump leaching (hereinafter collectively referred to as “heap leaching”) provide lower metal recoveries than other metallurgical process options for recovering copper from copper-containing ores, such as milling and flotation that produces copper-containing concentrates that are then smelted to produce copper metal.
Consequently, heap leaching tends to be reserved for lower grade ore types that have at least a proportion of readily recoverable copper, but where crushing/milling costs per unit of copper (or copper equivalent—i.e. when taking into account by-product credits from, for example, gold and silver) are too high to support a concentrator approach, or where mineral liberation and other characteristics (e.g. arsenic content) will not support production of directly useable or saleable concentrates.
Standard best industry practice is to use agglomerates of mined and thereafter crushed ore fragments in heaps. Typically, the mined ore is processed through multiple crushing steps, namely primary and secondary crushing steps, and in some instances tertiary crushing steps, and the crushed ore fragments are agglomerated in an agglomeration step, typically with the use of an acid.
The invention is concerned particularly with leaching mined and crushed and agglomerated ore fragments that contain chalcopyrite.
It is known that it is difficult to leach more than 20-40 wt. % of the total copper from chalcopyrite by heap leaching. The low copper recovery is often thought to be associated with the formation of a passive film on the surface of chalcopyrite.
International application PCT/AU2016/051024 in the name of the applicant relates to leaching chalcopyrite ores (and other copper-containing ores). The disclosure in the International application is incorporated herein by cross-reference.
An important focus of the International application is heap leaching fragments or agglomerates of fragments of chalcopyrite ores.
The International application describes and claims an invention that is based on a finding of the applicant, through a Group company of the applicant, that it is possible to achieve high (greater than 60 wt. % of the total copper) recovery of copper by leaching agglomerates of (a) fragments of chalcopyrite ores (and other copper-containing ores) and (b) silver.
The International application describes that the agglomerates may be formed by adding silver (a) to mined ore fragments prior to, or during, agglomeration of the ore fragments or (b) to already-formed agglomerates of the ore fragments.
In particular, as reported in the International application, the applicant found that low concentrations of silver, typically less than 2 g silver per kg copper in chalcopyrite ores, dispersed on the surfaces of chalcopyrite in agglomerates makes it possible to achieve higher recoveries (greater than 60 wt. %) of copper from the ores in shorter leaching times compared to leaching agglomerates that do not have silver dispersed in the agglomerates. This is a significant finding, particularly in the context of leaching lower grade chalcopyrite ores, i.e. ores containing less than 1.5 wt. % copper, typically less than 1.25 wt. % copper, and typically less than 1 wt. % copper, and typically less than 0.5 wt. % copper. This is also a significant finding in the context of leaching other lower grade copper-containing ores.
The present invention was made in the course of further research and development work in relation to the invention of the International application.
The present invention makes it possible to achieve higher recoveries of copper from chalcopyrite (and other copper-containing minerals) in ore fragments.
The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.